The present invention relates to a workpiece support structure for an ion beam implanter and, more particularly, to a workpiece support structure for an ion beam implanter including a hollow umbilical cord for routing coolant and electrical power between a rotatable workpiece support or pedestal of an electrostatic clamp within an evacuated implantation chamber and an exterior of the implanter at atmospheric pressure.
Ion beam implanters are widely used in the process of doping semiconductor wafers. An ion beam implanter generates an ion beam comprised of desired species of positively charged ions. The ion beam impinges upon an exposed surface of a workpiece such as a semiconductor wafer, substrate or flat panel, thereby xe2x80x9cdopingxe2x80x9d or implanting the workpiece surface with desired ions. The pedestal can be tilted to adjust an implantation angle of the workpiece with respect to the ion beam striking the workpiece. An implantation angle of zero degrees (0xc2x0) means that the implantation surface of the workpiece is normal to the ion beam beam path. To minimize the detrimental effects of channeling small positive and negative implantation angles are often used for implantation.
Some ion implanters utilize serial implantation wherein one relatively large wafer workpiece is positioned on a workpiece support or pedestal of an electrostatic chuck in an evacuated implantation chamber and implanted or xe2x80x9cdopedxe2x80x9d with desired ions. After implantation is completed, the workpiece is removed from the pedestal and another workpiece is positioned on the pedestal. In a quad implantation, a workpiece is subject to four implantations. Typically, after each of the four implantations the workpiece is rotated ninety degrees (90xc2x0).
The pedestal and electrostatic chuck are supported by a workpiece support structure extending into an evacuated implantation chamber. Specifically, the electrostatic chuck is supported on a scan arm. Certain facilities, including cooling fluid and gas and electrical power, must be routed to the electrostatic chuck pedestal through an interior region of the scan arm. The interior region of the scan arm is in communication with the outside environment and, therefore, is at atmospheric pressure. Since the pedestal rotates with respect to the scan arm, routing the facilities through the fixed scan arm to the rotating pedestal while maintaining a vacuum seal between the pedestal (at vacuum in the implantation chamber) and the scan arm interior region (at atmospheric pressure) is problematic.
One approach to providing for routing of the facilities to the pedestal while maintaining a vacuum seal between the pedestal and the scan arm interior region is to provide a slip ring and sliding seal assembly between the scan arm and the electrostatic chuck pedestal and route the facilities through the slip ring. However, such a slip ring and sliding seal assembly is bulky because of the xe2x80x9cstack heightxe2x80x9d of the motor (which rotates the pedestal), the slip ring and the sliding seal. The xe2x80x9cstack heightxe2x80x9d of such a slip ring/sliding seal assembly is relatively large whether the pedestal is driven by a direct drive motor affixed to the pedestal or the pedestal is driven by a motor and belt drive system wherein the motor is supported by the scan arm in a position offset from the pedestal. The slip ring/sliding seal assembly is also heavy and prone to leaking. Additionally, such assemblies often cause electrical breakdown or arcing and create excess drag to the mechanical drive system that rotates the pedestal.
What is desired is a workpiece support structure that provides for routing of facilities to the pedestal of an electrostatic chuck through an interior region of a scan arm supporting the electrostatic chuck that is less bulky, that is, has a shorter xe2x80x9cstack heightxe2x80x9d than the combined stack height of the pedestal drive motor, slip ring and sliding seal of a slip ring/sliding seal assembly. What is also desired is a workpiece support structure that provides for routing of facilities to the pedestal of an electrostatic chuck through an interior region of a scan arm supporting the electrostatic chuck that is more durable than a slip ring/sliding seal assembly.
The present invention concerns an ion beam implanter having a workpiece support structure for supporting a workpiece within a vacuum or implantation chamber. The ion beam implanter includes an ion beam source for generating an ion beam moving along a path of travel and being scanned along an axis. A wafer workpiece is supported by the workpiece support structure in the implantation chamber such that the workpiece is positioned to intersect the path of travel of the scanned ion beam for implantation of an implantation surface of the workpiece by the ion beam.
In one preferred embodiment of the present invention, the workpiece support structure includes a workpiece holder assembly including a rotatable pedestal and an electrostatic clamp or chuck supporting the workpiece. The workpiece support structure further includes a drive system or assembly for rotating the pedestal and the workpiece coupled thereto. The drive assembly includes a drive motor, a drive pulley, a driven pulley and a drive belt extending between the drive and driven pulleys. The drive pulley is coupled to the drive motor, the driven pulley is coupled to the pedestal. When the drive motor rotates, the drive pulley is rotated causing the drive belt to rotate the driven pulley and thereby also rotate the pedestal.
The workpiece support structure further includes a first rotatable reel coupled to the drive pulley, a second rotatable reel coupled to and rotatable with the pedestal and a flexible, hollow, facilities-routing cable or cord extending between the first and second rotatable reels and partially wrapped around at least one of the first and second reels such that, as the pedestal is rotated in a first direction, a length of the flexible cord wrapped around the first reel increases and a length of the flexible cord wrapped around the second reel decreases and, as the pedestal is rotated in an opposite direction, a length of the flexible cord wrapped around the first reel decreases and a length of the flexible cord wrapped around the second reel increases.
Facilities including one or more water and gas coolant lines carrying coolant to the electrostatic clamp and one or more electrical power conductors conducting electrical power to the clamp are disposed within and routed through the cord. The coolant lines include a water feed and gas feed for gas cooling. Preferably, a first connector assembly is disposed near an end of the cord attached to the first reel, the first connector assembly providing for fixed connections for the coolant lines and electrical power conductors routed through the cord and a second connector assembly is disposed near an end of the cord attached to the second reel, the second connector assembly also providing for a fixed connections for the coolant lines and electrical power conductors.
The workpiece support structure preferably further includes a support or scan arm that supports the chuck, the scan arm defining an interior region at atmospheric pressure, the first and second rotatable reels, the cord and the drive and driven pulleys are disposed within the scan arm interior region. Advantageously, a hollow vacuum seal is disposed between the driven pulley and the pedestal to provide a seal between the ion implantation chamber interior region and the scan arm interior region, the vacuum seal defining a central opening through which a portion of the facilities are routed to the pedestal and electrostatic clamp.
The workpiece support structure of the present invention routes facilities (coolant and electrical power) through the hollow, facilities-routing cord and the use of a flat, hollow vacuum seal between the driven pulley and the pedestal. This arrangement provides for a highly durable routing of facilities from outside the implantation chamber (at atmospheric pressure) to the pedestal inside the implantation chamber (at vacuum) because of the durability of the flexible cord compared to a slip ring assembly, while at the same time advantageously minimizing xe2x80x9cstack heightxe2x80x9d compared to motor plus a slip ring/sliding seal arrangement because the pedestal drive motor is offset from the pedestal-pulley vacuum seal and pedestal bearing assembly and a flat vacuum seal is used between the driven pulley and the pedestal. The workpiece support structure of the present invention also allows for a thinner scan arm and is better balanced because the pedestal drive motor is not positioned at the end of the scan arm where it would create additional torque forces on the scan arm. Yet another advantage of the workpiece support structure of the present invention is that it permits a stand-alone dosimetry system that monitors the ion beam to be positioned in dose proximity to the workpiece being implanted.
In a second preferred embodiment of the present invention, the workpiece support structure utilizes a single reel coupled to the pedestal. A hollow, facilities-routing cord, which routes facilities to the pedestal and the electrostatic chuck of the pedestal, is wound around the single reel, much like a clock spring. As the pedestal rotates in a first direction, the umbilical cord is unwrapped or played out from the reel, as the pedestal rotates in an opposite direction, the umbilical cord is wrapped or played onto the reel. As in the first preferred embodiment, a flat, hollow vacuum seal is disposed between the driven pulley and the pedestal. A driven pulley is coupled to the pedestal. A rotatable drive member is operatively connected to the driven pulley via a drive belt. As the rotatable drive member rotates, the driven pulley, umbilical cord reel and pedestal rotate in unison.
In a third preferred embodiment of the present invention, the workpiece support structure also utilizes a single reel coupled to the pedestal. The difference between the second and third embodiments is that a direct drive motor is coupled to the pedestal and the single reel obviating the need for a drive belt. As in the second preferred embodiment, a facilities-carrying, hollow cord is played onto and played out from the reel as the pedestal and reel are rotated in unison. A flat, hollow vacuum seal is disposed between reel and the pedestal. While in this embodiment, the direct drive motor positioned adjacent the pedestal does increase the stack height slightly and adds an additional torque force to a distal end of the scan arm, it simplifies the drive system by eliminating the need for a drive belt and driven pulley.
These and other objects, advantages, and features of the exemplary embodiment of the invention are described in detail in conjunction with the accompanying drawings.